Shore hardness of as-printed and dehydrated thermoplastic materials made using fused filament fabrication (FFF)

This article explores the Shore hardness (following ASTM D2240) of 10 common engineering plastics and chopped carbon fiber composites that have been processed using fused filament fabrication (FFF). The study was done in two parts, the first focusing on raw, as-printed specimens (typical use case for FFF parts) and the second looking at specimens that spent various lengths of time (4 h, 24 h, and 72 h) in a heated dehydration chamber. Extensive analyses of the collected data showed that dehydrating the samples had a statistically significant effect (based on 25 replications) in most cases, showing that the moisture content of tested FFF samples is an important factor in their characterization and use. For most of the materials, the hardness either plateaued or decreased after a certain dehydration time, suggesting that FFF parts are affected by both too much and too little moisture content. The study also included an extensive sensitivity analysis related to the required specimen thickness for valid hardness tests. In addition to providing useful new characterization data for the materials, the results of this study give design information that will be useful for material selection when using FFF as a manufacturing process.